The present invention relates to telephone digital switching systems and more particularly to a method and apparatus to determine whether a telephone subscriber line is loaded or non-loaded to enable automatic selection of the proper balance network for a two wire telephone loop or line in a digital switching system.
When operating a digital switching system it is necessary to select the proper balance network for the two-wire telephone loop to the subscriber. The most appropriate balance network must be selected to ensure proper operation of the system. Within the ITT 1210 digital switch these balance networks include the loaded network (1420 ohms in parallel with the build-out capacitor) a non-loaded network (690 ohms in parallel with a 0.056 microfarad capacitor) and the compromise network (900 ohms in series with a 2.14 microfarad capacitor). Currently, a digital switching system requires the customer to manually set the balance network which is located on the line printed circuit cards to the appropriate position for each loop. This entails a significant administration problem not only for the initial installation but also when any of the quad line cards are replaced.